Synthesis of 3-Phenylserine by a Two-enzyme Cascade System with PLP Cofactor.

A two-enzyme cascade system containing ω-transaminase (ω-TA) and L-threonine aldolase (L-ThA) was reported for the synthesis of 3-Phenylserine starting from benzylamine, and PLP was utilized as the only cofactor in these both two enzymes reaction system. Based on the transamination results, benzylamine was optimized as an advantageous amino donor as confirmed by MD simulation results. This cascade reaction system could not only facilitate the in situ removal of the co-product benzaldehyde, enhancing the economic viability of the reaction, but also establish a novel pathway for synthesizing high-value phenyl-serine derivatives. In our study, nearly 95 % of benzylamine was converted, yielding over 54 % of 3-Phenylserine under the optimized conditions cascade reaction.

Xylan cinnamoylation for reinforcing poly (butylene adipate-co-terephthalate): Molecule design and interaction optimization.

PBAT composites with biomass fillers have gained considerable attention as alternatives to non-biodegradable plastics. This work employed xylan derivatives as fillers for PBAT composites. Xylan was modified by introducing cinnamoyl side groups which limit the hydrogen bonding and construct π-π stacking interactions with PBAT chains. The resultant xylan cinnamates (XCi) show degree of substitution (DS) of 0.55-1.89, glass-transition temperatures (Tg) of 146.5-175.0 °C and increased hydrophobicity, which can be simply controlled by varying the molar ratio of reactants. NMR results demonstrate that the C3-OH of xylopyranosyl unit is more accessible to cinnamoylation. XCi fillers (30-50 wt%) were incorporated into PBAT through melt compounding. The filler with a DS of 0.97 exhibited the optimal reinforcing effect, showing superior tensile strength (19.4 MPa) and elongation at break (330.9 %) at a high filling content (40 wt%), which is even beyond the neat PBAT. SEM and molecular dynamics simulation suggest improved compatibility and strengthened molecular interaction between XCi and PBAT, which explains the suppressed melting/crystallization behavior, the substantial increase in Tg (-34.5 â†’ -1.8 °C) and the superior mechanical properties of the composites. This research provides valuable insights into the preparation of high-performance composites by designing the molecular architecture of xylan and optimizing the associated interactions.

Recent Advances of Lignin Functionalization for High-Performance and Advanced Functional Rubber Composites.

The biomass lignin is the only large-volume renewable feedstock that is composed of aromatics but has been largely underutilized and is sought for valorization as a value-added material. Recent research has highlighted lignin as a promising alternative to traditional petrol-based reinforcements and functional additives for rubber composites. This review summarized the recent advances in the functionalization of lignin for a variety of rubber composites, as well as the compounding techniques for effectively dispersing lignin within the rubber matrix. Significant progress has been achieved in the development of high-performance and advanced functional rubber/lignin composites through carefully designing the structure of lignin-based additives and the optimization of interfacial morphologies. This Review discussed the effect of lignin on composite properties, including mechanical reinforcement, dynamic properties, antiaging performance, and oil resistance, and also the advanced stimuli-responsive performance in detail. A critical analysis for the future development of rubber/lignin composites is presented as concluding remarks.

Engineering Saccharomyces cerevisiae for improved biofilm formation and ethanol production in continuous fermentation.

BACKGROUND: Biofilm-immobilized continuous fermentation has the potential to enhance cellular environmental tolerance, maintain cell activity and improve production efficiency. RESULTS: In this study, different biofilm-forming genes (FLO5, FLO8 and FLO10) were integrated into the genome of S. cerevisiae for overexpression, while FLO5 and FLO10 gave the best results. The biofilm formation of the engineered strains 1308-FLO5 and 1308-FLO10 was improved by 31.3% and 58.7% compared to that of the WT strain, respectively. The counts of cells adhering onto the biofilm carrier were increased. Compared to free-cell fermentation, the average ethanol production of 1308, 1308-FLO5 and 1308-FLO10 was increased by 17.4%, 20.8% and 19.1% in the biofilm-immobilized continuous fermentation, respectively. Due to good adhering ability, the fermentation broth turbidity of 1308-FLO5 and 1308-FLO10 was decreased by 22.3% and 59.1% in the biofilm-immobilized fermentation, respectively. Subsequently, for biofilm-immobilized fermentation coupled with membrane separation, the engineered strain significantly reduced the pollution of cells onto the membrane and the membrane separation flux was increased by 36.3%. CONCLUSIONS: In conclusion, enhanced biofilm-forming capability of S. cerevisiae could offer multiple benefits in ethanol fermentation.

Synthesis and Characterization of Novel Triphenylamine-Containing Electrochromic Polyimides with Benzimidazole Substituents.

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N'-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4'-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4'-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV-Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials.

High-Strength Bio-Degradable Polymer Foams with Stable High Volume-Expansion Ratio Using Chain Extension and Green Supercritical Mixed-Gas Foaming.

The preparation of biodegradable polymer foams with a stable high volume-expansion ratio (VER) is challenging. For example, poly (butylene adipate-co-terephthalate) (PBAT) foams have a low melt strength and high shrinkage. In this study, polylactic acid (PLA), which has a high VER and crystallinity, was added to PBAT to reduce shrinkage during the supercritical molded-bead foaming process. The epoxy chain extender ADR4368 was used both as a chain extender and a compatibilizer to mitigate the linear chain structure and incompatibility and improve the foamability of PBAT. The branched-chain structure increased the energy-storage modulus (G') and complex viscosity (η*), which are the key factors for the growth of cells, by 1-2 orders of magnitude. Subsequently, we innovatively used the CO2 and N2 composite gas method. The foam-shrinkage performance was further inhibited; the final foam had a VER of 23.39 and a stable cell was obtained. Finally, after steam forming, the results showed that the mechanical strength of the PBAT/PLA blended composite foam was considerably improved by the addition of PLA. The compressive strength (50%), bending strength, and fracture load by bending reached 270.23 kPa, 0.36 MPa, and 23.32 N, respectively. This study provides a potential strategy for the development of PBAT-based foam packaging materials with stable cell structure, high VER, and excellent mechanical strength.

Study on lignin amination for lignin/SiO2 nano-hybrids towards sustainable natural rubber composites.

Lignin-based hybrid fillers are of increasing importance with regards to the valorization of low-value biomass and the requirement of sustainability in rubber industry, however, a facile lignin modification approach tuning the supramolecular interactions to favor the assembly of the hybrids is in demand. This study aimed to design a lignin/SiO2 nano-hybrid via an in-situ assembly of diethylamine grafted lignin (DL) and SiO2, and investigate its reinforcing effect on natural rubber (NR). DL was prepared through Mannich modification of lignin, and the grafted diethylamine can be clearly identified by FTIR, NMR and elemental analysis. The resultant hybrid (DLSi) displays as homogeneous nanospheres with well integrated DL and SiO2 components as shown in the TEM images, and the hybrid (DLSi1) prepared with weight ratio of DL/SiO2 = 1/2 shows a minimum particle size of 101.8 nm and significantly reduced polarity. Compared to the reference composite filled only with carbon black (CB), NR composites filled with DLSi/CB of 10/40 phr shows comparable mechanical properties and reduced rolling resistance, which is due to the low particle size, homogenous dispersion and strong rubber-filler interfacial affinity. Such remarkable performance suggests that the DLSi hybrid can be a promising versatile biobased filler for the application in gasoline-saving "green" tires.

College students' anxiety after returning to school during the COVID-19 epidemic: What should we care.

The college students' anxiety during the Coronavirus disease 2019 (COVID-19) epidemic remains unclear. We aimed to evaluate the college students' anxiety after returning to school during the COVID-19 epidemic, to provide reference for the management and nursing care of college students. We conducted a survey from September 15, 2021 to September 30, 2021 investigate the anxiety level of college students. The Self-rating Anxiety Scale was used for anxiety assessment. The Spearman correlation analysis was conducted to evaluate the correlation between students' anxiety and characteristics. Logistic regression analysis was used to explore the influencing factors of concurrent anxiety among college students. A total of 2168 college students were included, the incidence of anxiety was 30.07% in college students during the COVID-19 epidemic. Pearson correlation analyses showed that grade (R = 0.715), main use of computer and mobile phone (R = 0.622), daily exercise (R = 0.735), whether relatives or friends are infected with COVID-19 (R = 0.735) are associated with the anxiety level of college students (all P < .05). Logistic regression analysis indicated that senior year (Odds ratio [OR] = 2.064, 95% confidence interval [CI]: 1.355-3.001), online game (OR = 3.122, 95% CI: 2.562-3.899), relatives or friends are infected with COVID-19 (OR = 2.987, 95% CI: 1.901-3.451) are the independent risk factors of anxiety in college students (all P < .05). Daily exercise (OR = 0.514, 95% CI: 0.205-0.814) was the independent protective factors of anxiety in college students (P = .008). During the COVID-19 epidemic, college students have increased anxiety and there are many influencing factors. Administrators and educators should especially pay attention to the mental health of students with those risk factors to maintain students' physical and mental health.

Reversible Adsorption and Detachment of Saccharomyces cerevisiae on Thermoresponsive Poly(N-isopropylacrylamide)-Grafted Fibers for Continuous Immobilized Fermentation.

Biofilm-mediated continuous fermentation with cells immobilized has gained much attention in recent years. In this study, thermoresponsive poly(N-isopropylacrylamide)-grafted cotton fibers (PNIPAM-CF) were prepared via an improved surface-initiated atom transfer radical polymerization. The modification process imparted switchable wettability to the surface while maintaining the thermal stability and biocompatibility of the CF. During the ethanol transformation, the rapid, reversible cell adsorption and detachment of Saccharomyces cerevisiae were performed through the modulation of wettability, displaying the enhancement of immobilized biomass and immobilization efficiency from 2.20 g/L and 59.43% to 2.81 g/L and 93.32%, respectively. Moreover, the biofilm adsorption matched well with the Freundlich model, indicating that multilayer adhesion was the main mode of biofilm formation. Based on the accumulation of the biofilm, the fabrication and utilization of PNIPAM-CF improved the efficiency of continuous immobilized fermentation, making the ethanol production reach 26.34 g/L in the sixth batch of fermentation. Meanwhile, wettability regulation further enhanced the reusability of the carrier. Therefore, the findings of this study revealed that the application of smart materials in cell immobilization systems had broad prospects for achieving sustainable and continuous catalysis.

Design and optimization of the continuous separation process for lignin and alkali by 'Extended Separation Volume' method.

This work is to design and optimize the 4column-simulated moving bed unit to separate and recovery alkali and lignin from black liquor. Since both alkali lignin and NaOH are the main products, we proposed the 'extended separation volume' methodology to construct a four-dimensional separation region (QI×QII×QIII×QIV) to design the operating conditions. Special attention was paid to investigate the influence of flow-rates in each zone on the performance parameters of these two products. The results show besides QII and QIII, QI and QIV can affect the concentrations and productivities significantly and have to be taken into account. Afterwards, the Response Surface Methodology, conducted by Design-Expert® was chosen to deal with the multi-objective optimization problem. The unique optimal operating conditions were finally obtained with the concentration of 74.7% and 48.1% of feed solution, and the productivity of 3.9 and 0.7 g/(L·h)-1 for alkali lignin and NaOH. Considering the actual operation, the productivity of 2.5 and 0.446 g/(L·h)-1 were obtained by experiment of internal actual operation point.

Ultrafine particles exposure is associated with specific operative procedures in a multi-chair dental clinic.

Air quality in dental clinics is critical, especially in light of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic, given that dental professionals and patients are at risk of regular exposure to aerosols and bioaerosols in dental clinics. High levels of ultrafine particles (UFP) may be produced by dental procedures. This study aimed to quantify ultrafine particles (UFP) concentrations in a real multi-chair dental clinic and compare the levels of UFP produced by different dental procedures. The efficiency of a high-volume evacuator (HVE) in reducing the UFP concentrations during dental procedures was also assessed. UFP concentrations were measured both inside and outside of a dental clinic in Shanghai, China during a 12-day period from July to September 2020. Dental activities were recorded during working hours. The mean (±standard deviation) concentrations of indoor and outdoor UFP during the sampling period were 8,209 (±4,407) counts/cm3 and 15,984 (±7,977) counts/cm3, respectively. The indoor UFP concentration was much higher during working hours (10,057 ± 5,725 counts/cm3) than during non-working hours (7,163 ± 2,972 counts/cm3). The UFP concentrations increased significantly during laser periodontal treatment, root canal filling, tooth drilling, and grinding, and were slightly elevated during ultrasonic scaling or tooth extraction by piezo-surgery. The highest UFP concentration (241,136 counts/cm3) was observed during laser periodontal treatment, followed by root canal filling (75,034 counts/cm3), which showed the second highest level. The use of an HVE resulted in lower number concentration of UFP when drilling and grinding teeth with high-speed handpieces, but did not significantly reduce UFP measured during laser periodontal therapy. we found that many dental procedures can generate high concentration of UFP in dental clinics, which may have a great health impact on the dental workers. The use of an HVE may help reduce the exposure to UFP during the use of high-speed handpieces.

Cooperative chemoenzymatic synthesis of N-heterocycles via synergizing bio- with organocatalysis.

Inspired by Nature's ingenuity, considerable progress has been made in recent years to develop chemoenzymatic processes by the integration of environmentally friendly feature of biocatalysis with versatile reactivity of chemocatalysis. However, the current types of chemoenzymatic processes are relatively few and mostly rely on metal catalysts. Here, we report a previously unexplored cooperative chemoenzymatic system for the synthesis of N-heterocycles. Starting from alcohols and amines, benzimidazole, pyrazine, quinazoline, indole, and quinoline can be obtained in excellent yields in water with O2 as the terminal oxidant. Synthetic bridged flavin analog is served as a bifunctional organocatalyst for the regeneration of cofactor nicotinamide adenine dinucleotide in the bioprocess and oxidative cyclodehydrogenation in the chemoprocess. Compared to the classical acceptorless dehydrogenative coupling strategy, being metal and base free, requiring only water as solvent, and not needing atmosphere protection were observed for the present method, exhibiting a favorable green and sustainable alternative.

Physiological changes and growth behavior of Corynebacterium glutamicum cells in biofilm.

Biofilm cells are well-known for their increased survival and metabolic capabilities and have been increasingly implemented in industrial and biotechnological processes. Corynebacterium glutamicum is one of the most widely used microorganisms in the fermentation industry. However, C. glutamicum biofilm has been rarely reported and little is known about its cellular basis. Here, the physiological changes and characteristics of C. glutamicum biofilm cells during long-term fermentation were studied for the first time. Results showed that the biofilm cells maintained stable metabolic activity and cell size was enlarged after repeated-batch of fermentation. Cell division was slowed, and chromosome content and cell proliferation efficiency were reduced during long-term fermentation. Compared to free cells, more biofilm cells were stained by the apoptosis indicator dyes Annexin V-FITC and propidium iodide (PI). Overall, these results suggested slow-growing, long-lived cells of C. glutamicum biofilm during fermentation, which could have important industrial implications. This study presents first insights into the physiological changes and growth behavior of C. glutamicum biofilm cell population, which would be valuable for understanding and developing biofilm-based processes.

Amphiphilic Nanointerface: Inducing the Interfacial Activation for Lipase.

Graphene-based materials are widely used in the field of immobilized enzymes due to their easily tunable interfacial properties. We designed amphiphilic nanobiological interfaces between graphene oxide (GO) and lipase TL (Thermomyces lanuginosus) with tunable reduction degrees through molecular dynamics simulations and a facile chemical modulation, thus revealing the optimal interface for the interfacial activation of lipase TL and addressing the weakness of lipase TL, which exhibits weak catalytic activity due to an inconspicuous active site lid. It was demonstrated that the reduced graphene oxide (rGO) after 4 h of ascorbic acid reduction could boost the relative enzyme activity of lipase TL to reach 208%, which was 48% higher than the pristine GO and 120% higher than the rGO after 48 h of reduction. Moreover, TL-GO-4 h's tolerance against heat, organic solvent, and long-term storage environment was higher than that of free TL. The drawbacks of strong hydrophobic nanomaterials on lipase production were explored in depth with the help of molecular dynamics simulations, which explained the mechanism of enzyme activity enhancement. We demonstrated that nanomaterials with certain hydrophilicity could facilitate the lipase to undergo interfacial activation and improve its stability and protein loading rate, displaying the potential of the extensive application.

A Hemicyanine-Assembled Upconversion Nanosystem for NIR-Excited Visualization of Carbon Monoxide Bio-Signaling In Vivo.

Carbon monoxide (CO) is considered as the second gasotransmitter involved in a series of physiological and pathological processes. Although a number of organic fluorescent probes have been developed for imaging CO, these probes display excitation within the ultraviolet or visible range, which restrict their applications in the complex biosystems. In the present work, a strategy is developed to construct an upconversion nanoparticles-based nanosystem for upconversion luminescent (UCL) sensing CO. This nanosystem exhibits a fast response to CO with high sensitivity and selectivity in aqueous solution by a near-infrared-excited ratiometric UCL detection method. Meanwhile, laser scanning upconversion luminescence microscope experiments demonstrate that this nanosystem can visualize the endogenous CO bio-signaling in living cells, deep tissues, zebrafish, and living mice by ratiometric UCL imaging. In particular, this nanosystem has been successfully employed in visualization of the endogenous CO bio-signaling through up-regulation of heme oxygenase-1 (HO-1) in the progression of hypoxia, acute inflammation, or ischemic injury. This work demonstrates that the outstanding performance of the nanosystem not only can provide an effective tool for further understanding the role of CO in the physiological and pathological environment, but also may have great potential ability for tracking the expression of HO-1 in living systems.

Stabilizing bienzymatic cascade catalysis via immobilization in ZIF-8/GO composites obtained by GO assisted co-growth.

Enzyme catalysis has clear advantages in the process of oxidizing glucose to produce gluconic acid. In the enzyme cascade, the improvement of the cascade efficiency is desired but challenging. Graphene oxide (GO) and ZIF-8 composites as enzyme support offer the promising opportunity that not only the cascade efficiency can be improved by control the distance between two enzymes, but also the stability can be improved. Here, a new strategy of GO assisted co-growth of ZIF-8 and enzyme was carried in a one-pot synthesis. Glucose oxidase&catalase immobilized in the ZIF-8/GO composites can obtain 98% residual activity after 15 days of storage with almost no enzyme shedding. The residual activity is still higher than 75% after 5 repeated uses. The presented method of controllable growth of metal organic frameworks on 2D nanosheet can also be extended for renewable energy devices, gas storage and separation of small molecules.

Constructing a multienzyme cascade redox-neutral system for the synthesis of halogenated indoles.

Inspired by biocatalytic retrosynthesis, a multienzyme cascade system containing alcohol dehydrogenase, flavin-dependent halogenase and flavin reductase was developed for the synthesis of several halogenated indoles starting from amino alcohol. This redox-neutral system not only omitted co-substrate for nicotinamide cofactor (NADH) regeneration but also showed relatively higher conversion and chemoselectivity compared with individual biotransformation. Artificial nicotinamide cofactor (BNAH) was employed to replace NADH and flavin reductase for simplifying this system, providing a more convenient strategy for halogenated indoles.

MTHFD2 promotes ovarian cancer growth and metastasis via activation of the STAT3 signaling pathway.

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) is a bifunctional enzyme located in the mitochondria. MTHFD2 has been reported to be overexpressed in several malignant tumors and is implicated in cancer development. This study aimed to investigate the effect of MTHFD2 on ovarian cancer progression. The expression of MTHFD2 was detected by bioinformatic analysis, immunohistochemistry, RT-qPCR (real-time quantitative PCR analysis), and western blot analysis. The effects of MTHFD2 depletion on cell proliferation, migration, and invasion were determined through in vitro experiments. Cell cycle progression and apoptosis were accessed by flow cytometry. The related signaling pathway protein expression was determined by western blot analysis. We found that MTHFD2 is highly expressed in both ovarian cancer tissues and cell lines. MTHFD2 deletion suppressed cell proliferation and metastasis. Knockdown of MTHFD2 induces cell apoptosis and G2/M arrest, whereas the number of cells in S phase increased with MTHFD2 overexpression. Mechanically, our results indicate that an inhibitory effect of MTHFD2 knockdown may be mediated by the downregulation of cyclin B1/Cdc2 complex and the inhibitory effect on its activity. Additionally, MTHFD2 could regulate cell growth and aggressiveness via activation of STAT3 and the STAT3-induced epithelial-mesenchymal transition signaling pathway. These findings indicate that MTHFD2 is overexpressed in ovarian cancer and regulates cell proliferation and metastasis, presenting an attractive therapeutic target.

Improved adenylate cyclase activity via affinity immobilization onto co-modified GO with bio-inspired adhesive and PEI.

Adenylate cyclase (AC) can efficiently catalyze the conversion of adenosine triphosphate (ATP) to cyclic adenosine-3', 5'-monophosphate (cAMP). However, AC directly immobilized on substrate is not desirable due to enzyme inactivation. Herein, bio-inspired adhesive of polydopamine and polyethyleneimine (PDA/PEI) was used as flexible chains to graft on graphene oxide (GO), and the AC was directionally immobilized through affinity between metal ions and his-tags of AC. The properties of modified GO and the activity of immobilized AC were studied in detail. PDA/PEI layers have been proved to improve the amino density of GO surface for affinity groups decoration and adjust the interaction between AC and support. And modified GO by this novel method contributes to subsequent grafting and immobilization of AC by affinity. AC immobilized on modified GO exhibited high activity recovery with about 90 % of free AC, while enzyme immobilized on unmodified GO has been inactivated. This study offers a versatile approach for support modification and enzyme oriented immobilization. PDA/PEI functionalized GO can be used as a promising carrier to immobilize other his-tagged enzymes.

Comparisons of nitrite accumulation, microbial behavior and nitrification kinetic in continuous stirred tank (ST) and plug flow (PF) moving bed biofilm reactors.

Two types of continuous stirred tank moving bed biofilm reactors (ST-MBBR) and plug flow MBBR (PF-MBBR) were compared for nitrification. PF-MBBR showed strong shock resistance to temperature, and ammonium oxidation ratio (AOR) was 9.63% higher than that in the ST-MBBR, although the average biomass and biofilm thickness of ST-MBBR were 7.32-18.59%, 9.44-14.06% higher than those in the PF-MBBR. Meanwhile, a lower nitrite accumulation ratio (NAR) was observed (54.88%) in the PF-MBBR than the ST-MBBR (78.92%) due to different operation modes, and the divergence was demonstrated by the microbial quantitative analysis. Nitrification kinetics revealed that the temperature coefficient (θ) in the ST-MBBR (1.068) was much higher than that in the PF-MBBR (1.006-1.015), proving the contrasting nitrification performances caused by temperature shock. According to the Monod equation, the half-saturation coefficient (KN) in the ST-MBBR was 0.19 mg/L while it varied around 0.12-0.24 mg/L in the PF-MBBR, revealing various NH4+ affinity owing to different biofilm thickness and microbial composition. Finally, MBBR optimization related to operation mode, temperature, and free ammonium (FA) inhibition for nitrite accumulation was discussed.